1. Field of the Invention
The present invention relates to an active-matrix liquid crystal display (LCD), and particularly, to an active-matrix LCD capable of reducing cross-talk and correctly displaying brightness according to display data.
2. Description of the Related Art
Each cell of an active-matrix LCD is equivalent to a capacitor having an end connected to a common voltage and another end to a TFT. Each cell has a cell electrode that may form parasitic capacitors with adjacent data and scan lines. When a scan pulse is applied to a scan line, TFTs of a row of cells connected to the scan line are turned on to connect cell electrodes of the cells to data lines, respectively. Then, data voltages are applied to the data lines to charge the cells. When the scan pulse disappears, the TFTs are turned off, and the cells sustain the applied voltages until the next scan pulse is applied thereto. A time necessary to write display data to a whole screen is called a frame, and each scan line receives a scan pulse per frame. Namely, each cell is written frame by frame.
A voltage sustained by a given cell controls liquid crystals of the cell. The display quality of the LCD is dependent on whether or not each cell thereof correctly sustains an applied voltage for a period between scan pulses. An off current of the TFT of the cell can fluctuate the sustained voltage. To suppress such a fluctuation, it is usual to provide each cell with an accumulation capacitor. The accumulation capacitor is formed by overlaying the cell electrode on an adjacent scan line or on a dedicated accumulation capacitor electrode. The accumulation capacitor, however, is incapable of completely eliminating the fluctuation because it is caused by various reasons. It is required to provide an LCD driving method or structure capable of correctly sustaining cell voltages.
The scan pulse also fluctuates the voltage sustained by a cell. Since this kind of fluctuation is constant, it can be canceled by adjusting a voltage applied to a counter electrode of each cell or by correcting a data voltage applied to each cell. An object of the present invention is to eliminate a fluctuation in the sustained voltage due to data voltages applied to adjacent data lines of each cell, and therefore, this kind of fluctuation, which is called cross-talk, is mainly explained.
When cross-talk occurs on a given cell due to data voltages applied to other cells that are connected to the data line to which the given cell is connected, it is called vertical cross-talk. When cross-talk occurs on a given cell due to data voltages applied to adjacent data lines of the given cell, it is called horizontal cross-talk. The magnitude of cross-talk is determined by the ratio of the parasitic capacitance of a cell to the total capacitance thereof. The parasitic capacitance is produced between the cell and adjacent data lines. To reduce the cross-talk, the parasitic capacitance must be reduced. For this purpose, a prior art forms a dedicated accumulation capacitor electrode in each cell. This electrode, however, needs a space that reduces an aperture of the cell to lower the brightness. To compensate for the brightness loss, it is necessary to employ strong illumination, which increases power consumption and is disadvantageous for a portable LCD that must be bright at low power consumption. There is a large-aperture LCD that forms each cell electrode over adjacent data lines. This LCD, however, produces large parasitic capacitance between each cell and adjacent data lines, which enlarges cross-talk.